The influence of extrusion on loss and racemization of amino acids

Abstract

The influence of the operation conditions (temperature and residence time) of a thermic treatment on the total amount (free and protein-bound) of amino acid enantiomers of dry fullfat soya was investigated. Total amino acid content was determined using conventional ion-exchange amino acid analysis of total hydrolysates and chiral amino acid analysis was performed by HPLC after precolumn derivatization with o-phthaldialdehyde and 1-thio-beta-D-glucose tetraacetate. Contrary to corn that was investigated previously, notable racemization was detected even at lower temperatures. At 140 degrees C the ratio of the D-enantiomer was 0.87% for glutamic acid, 2.81% for serine, and 1.92% for phenylalanine; at 220 degrees C the ratios of the D-enantiomer of the above amino acids were 1.43, 4.61, and 4.68%, respectively. The concentration of several L-amino acids decreased. At 220 degrees C there was 10% less L-glutamic acid, 17% less L-serine, 5% less L-phenylalanine, 6.6% less L-aspartic, acid and 21% less L-lysine than in the control; their loss can be assigned to different degrees of L - D conversion. While nearly complete transformation of L-phenylalanine can be attributed to racemization, the main cause of the loss of L-lysine is not racemization. The treatments in the same order of magnitude resulted in the formation of more D-amino acids and greater extent of racemization of amino acids in fullfat soya than that of maize.

Extruded soybean meal increased feed intake and milk production in dairy cows

“…A similar decrease in Lys concentration of SBM with increasing the heating temperature above 160°C was also observed in the pilot study reported in Figure 2. These effects have been attributed to formation of Maillard products and cross links among AA (Björck and Asp, 1983;Csapó et al, 2008).…”

Origin, Microbiology, Nutrition, and Pharmacology of D‐Amino Acids

“…Racemization rates of the same amino acid in polyamino acids were much lower than in soy proteins. Related studies [93] showed that: free amino acids racemized approximately ten times slower than did proteinbound ones; alkali treatment of zein induced racemization of amino acids residues and caused nutritional damage without the presence of lysinoalanine (LAL) [94]; serine residues in lactalbumin, leaf protein concentrate, and soy protein were highly susceptible to heat-and alkali-induced racemization [95]; racemization of protein-bound amino acids, especially of lysine, induced by heat extrusion was greater in soy than in corn proteins [96]; melanoidins formed during heating of glucose or fructose with LAA or DAA had similarly shaped but different absorption spectra [97].…”

Simultaneous Determination of L- and D-Amino Acids in Proteins: A Sensitive Method Using Hydrolysis in Deuterated Acid and Liquid Chromatography–Tandem Mass Spectrometry Analysis

“…Chemical hydrolysis (acid or alkaline) will result in a (partial) racemization of the amino acids, where L-amino acids are converted to D-amino acids and vice versa [22]. The degree of racemization depends on hydrolysis conditions, including temperature, pressure, time and chemical composition of the hydrolysis solution, as well as the individual amino acids [2,3,22]. Therefore, analysis of the L-and D-amino acid composition of hydrolyzed samples may be biased.…”

“…Industrial processing or fermentation can lead to an increase in D-amino acid levels in food and feed proteins [1][2][3][4]. Consequently, the digestibility and bioavailability of these proteins decrease.…”

“…Food and feed proteins usually contain a very low amount of D-amino acids. The content of D-amino acids in feed [1] and foods can increase due to industrial processing, including; high temperature, extrusion or acid/alkaline treatment [2][3][4]. Fermented foods, certain health foods, and in some cases adulteration of non-fermented foods, are also known to contain higher levels of D-amino acids than fresh food [2,[5][6][7].…”